Current sensing schemes for accurate high current measurement are invariably bulky, expensive and/or power consuming. Shunts, magnetic amplifiers and Hall-effect transducers are commonly used despite concessions which must be made in each case. Shunts are bulky, concentrated heat sources that must be installed by breaking the power line. Magnetic amplifiers are expensive and generally require several watts of power for operation. Hall-effect transducers require by-pass currents on the order of 0.1 to 0.5 amperes and typically 2 to 10 watts total power.
To avoid these deficiencies, I have devised a method and apparatus for measuring current flow by taking voltage measurements on the conductor itself. In the preferred embodiment electrical leads are woven into an existing power cable at two spaced-apart points on the cable. Another lead is woven into the other power cable to provide power to the current measuring apparatus. A differential amplifier senses the voltage difference between the electrical leads from the two spaced-apart points and produces an output voltage signal representative of the current in the first cable. To correct for temperature-induced resistivity changes, at least one temperature dependent element is attached to the first cable at a point which has a temperature approximately the same as that between the two electrical connections thereto.